Buggy code:
public class CassandraServer implements Cassandra { private static Logger logger = LoggerFactory . getLogger ( CassandraServer . class ) ; private static final GenericArray < Column > EMPTY_SUBCOLUMNS = new GenericData . Array < Column > ( 0 , Schema . createArray ( Column . SCHEMA$ ) ) ; private static final GenericArray < ColumnOrSuperColumn > EMPTY_COLUMNS = new GenericData . Array < ColumnOrSuperColumn > ( 0 , Schema . createArray ( ColumnOrSuperColumn . SCHEMA$ ) ) ; private static final Utf8 API_VERSION = new Utf8 ( "0.0.0" ) ; private static final String D_CF_CFTYPE = "Standard" ; private static final String D_CF_CFCLOCKTYPE = "Timestamp" ; private static final String D_CF_COMPTYPE = "BytesType" ; private static final String D_CF_SUBCOMPTYPE = "" ; private static final String D_CF_RECONCILER = null ; public static final String D_COLDEF_INDEXTYPE = "KEYS" ; public static final String D_COLDEF_INDEXNAME = null ; public final ThreadLocal < ClientState > clientState = new ThreadLocal < ClientState > ( ) { @ Override public ClientState initialValue ( ) { } } ; private final IRequestScheduler requestScheduler ; public CassandraServer ( ) { } public Void login ( AuthenticationRequest auth_request ) throws AuthenticationException , AuthorizationException { } public ClientState state ( ) { } @ Override public ColumnOrSuperColumn get ( ByteBuffer key , ColumnPath columnPath , ConsistencyLevel consistencyLevel ) throws AvroRemoteException , InvalidRequestException , NotFoundException , TimedOutException , UnavailableException { } protected Map < DecoratedKey < ? > , ColumnFamily > readColumnFamily ( List < ReadCommand > commands , ConsistencyLevel consistency ) throws InvalidRequestException , TimedOutException , UnavailableException { } private List < Column > avronateSubColumns ( Collection < IColumn > columns ) { } private GenericArray < ColumnOrSuperColumn > avronateColumns ( Collection < IColumn > columns , boolean reverseOrder ) { } private GenericArray < ColumnOrSuperColumn > avronateSuperColumns ( Collection < IColumn > columns , boolean reverseOrder ) { } private GenericArray < ColumnOrSuperColumn > avronateColumnFamily ( ColumnFamily cf , boolean subColumnsOnly , boolean reverseOrder ) { } public List < ColumnOrSuperColumn > get_slice ( ByteBuffer key , ColumnParent columnParent , SlicePredicate predicate , ConsistencyLevel consistencyLevel ) throws AvroRemoteException , InvalidRequestException , TimedOutException , UnavailableException { } private List < CoscsMapEntry > multigetSliceInternal ( String keyspace , List < ByteBuffer > keys , ColumnParent columnParent , SlicePredicate predicate , ConsistencyLevel consistencyLevel ) throws InvalidRequestException , TimedOutException , UnavailableException { } private List < CoscsMapEntry > getSlice ( List < ReadCommand > commands , ConsistencyLevel consistencyLevel ) throws InvalidRequestException , TimedOutException , UnavailableException { } public int get_count ( ByteBuffer key , ColumnParent columnParent , SlicePredicate predicate , ConsistencyLevel consistencyLevel ) throws AvroRemoteException , InvalidRequestException , TimedOutException , UnavailableException { } public List < CoscsMapEntry > multiget_slice ( List < ByteBuffer > keys , ColumnParent columnParent , SlicePredicate predicate , ConsistencyLevel consistencyLevel ) throws AvroRemoteException , InvalidRequestException , TimedOutException , UnavailableException { } public Void insert ( ByteBuffer key , ColumnParent parent , Column column , ConsistencyLevel consistencyLevel ) throws AvroRemoteException , InvalidRequestException , TimedOutException , UnavailableException { } public Void remove ( ByteBuffer key , ColumnPath columnPath , long timestamp , ConsistencyLevel consistencyLevel ) throws AvroRemoteException , InvalidRequestException , TimedOutException , UnavailableException { } private void doInsert ( ConsistencyLevel consistency , RowMutation rm ) throws TimedOutException , UnavailableException { } public Void batch_mutate ( List < MutationsMapEntry > mutationMap , ConsistencyLevel consistencyLevel ) throws AvroRemoteException , InvalidRequestException , TimedOutException , UnavailableException { } private static RowMutation getRowMutationFromMutations ( String keyspace , ByteBuffer key , Map < CharSequence , List < Mutation > > cfMap ) { } private static void addColumnOrSuperColumnToRowMutation ( RowMutation rm , String cfName , ColumnOrSuperColumn cosc ) { } private static void deleteColumnOrSuperColumnToRowMutation ( RowMutation rm , String cfName , Deletion del ) { } private static void applyMigrationOnStage ( final Migration m ) throws InvalidRequestException { } private org . apache . cassandra . thrift . ConsistencyLevel thriftConsistencyLevel ( ConsistencyLevel consistency ) { } public Void set_keyspace ( CharSequence keyspace ) throws InvalidRequestException { } public CharSequence system_add_keyspace ( KsDef ksDef ) throws AvroRemoteException , InvalidRequestException { } public CharSequence system_add_column_family ( CfDef cfDef ) throws AvroRemoteException , InvalidRequestException { } public CharSequence system_update_column_family ( CfDef cf_def ) throws AvroRemoteException , InvalidRequestException { checkKeyspaceAndLoginAuthorized ( WRITE ) ; if ( ( ( cf_def . keyspace ) == null ) || ( ( cf_def . name ) == null ) ) throw newInvalidRequestException ( "Keyspace<seq2seq4repair_space>and<seq2seq4repair_space>CF<seq2seq4repair_space>name<seq2seq4repair_space>must<seq2seq4repair_space>be<seq2seq4repair_space>set." ) ; CFMetaData oldCfm = DatabaseDescriptor . getCFMetaData ( CFMetaData . getId ( cf_def . keyspace . toString ( ) , cf_def . name . toString ( ) ) ) ; if ( oldCfm == null ) throw newInvalidRequestException ( "Could<seq2seq4repair_space>not<seq2seq4repair_space>find<seq2seq4repair_space>column<seq2seq4repair_space>family<seq2seq4repair_space>definition<seq2seq4repair_space>to<seq2seq4repair_space>modify." ) ; try { oldCfm . apply ( cf_def ) ; <START_BUG> UpdateColumnFamily update = new UpdateColumnFamily ( CFMetaData . convertToThrift ( cf_def ) ) ; <END_BUG> CassandraServer . applyMigrationOnStage ( update ) ; return DatabaseDescriptor . getDefsVersion ( ) . toString ( ) ; } catch ( ConfigurationException e ) { InvalidRequestException ex = newInvalidRequestException ( e . getMessage ( ) ) ; ex . initCause ( e ) ; throw ex ; } catch ( IOException e ) { InvalidRequestException ex = newInvalidRequestException ( e . getMessage ( ) ) ; ex . initCause ( e ) ; throw ex ; } } public CharSequence system_update_keyspace ( KsDef ks_def ) throws AvroRemoteException , InvalidRequestException { } public GenericArray < CharSequence > describe_keyspaces ( ) throws AvroRemoteException { } public Utf8 describe_cluster_name ( ) throws AvroRemoteException { } public Utf8 describe_version ( ) throws AvroRemoteException { } public Map < CharSequence , List < CharSequence > > check_schema_agreement ( ) { } protected void checkKeyspaceAndLoginAuthorized ( Permission perm ) throws InvalidRequestException { } private void schedule ( ) { } private void release ( ) { } private CFMetaData convertToCFMetaData ( CfDef cf_def ) throws InvalidRequestException , ConfigurationException { } public KsDef describe_keyspace ( CharSequence keyspace ) throws AvroRemoteException , NotFoundException { } public CharSequence system_drop_column_family ( CharSequence column_family ) throws AvroRemoteException , InvalidRequestException { }

Fix:
UpdateColumnFamily update = new UpdateColumnFamily ( cf_def ) ;